(1) Field of the Invention
The present invention relates to the inspection of elongated members a particularly to the non-destructive testing of rails of the type employed to form railroad tracks. More specifically, this invention is directed to ultrasonic rail-flaw inspection equipment suitable for continuous field testing of rails. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
It is well known that safe and economic railway system operations requires the periodic inspection of rails in an effort to detect flaws. Failure to replace a rail section which has developed a flaw may result in the rail breaking which, in turn, may cause a derailment. To be feasible, rail flaw inspection equipment must be capable of continuous operation wherein equipment is moved along the test rail at a reasonable speed. Over the years, numerous non-destructive rail testing techniques have been proposed. The present state-of-the-art is represented by ultrasonic inspection apparatus such as, for example, exemplified by U.S. Pat. Nos. 3,028,751, 3,028,906, and 4,044,594.
A principal requirement for ultrasonic rail-flaw inspection equipment is that the transducer, which alternatively generates the ultrasound energy and/or receives echoes from within the object under test and converts these echoes into electrical signals, must be positioned laterally with respect to the rail so as to transmit and receive ultrasonic signals through the web of the rail. This critical position must be maintained regardless of rail curvature and wear. Accordingly, it is conventional practice to mount the ultrasonic flaw detection device transducer on a carriage which has provision to make lateral transducer adjustments with respect to each rail. While several concepts for automatic transducer carriage lateral position control have been proposed, to date none of these concepts have proved to be successful. The lack of automatic carriage position control has resulted in the average operating speed of present ultrasonic rail-flaw inspection equipment being severely limited because almost all decisions with respect to carriage position must be made by an operator who must also control the system manually. Thus, particularly when entering and leaving curves and when operating on badly worn rails, present ultrasound rail-flaw inspection equipment will either be inoperative because of lateral misalignment or the speed of testing must be reduced to an unacceptable slow rate in order to permit manual maintenance of the requisite alignment of the transducer with the rail web.
Prior proposals for automatic transducer carriage control for ultrasonic rail-flaw inspection equipment have suggested the use of sensors which reference position from outside surfaces of the rail head. This mode of operation, however, has not proven to be successful since, due to wear, the location of the exterior of the rail head does not always locate the acoustic center and coincide with the transducer located required to transmit and receive ultrasonic signals through the web of the rail. Oscillating carriage type systems have also been proposed such as, for example, the system of FIG. 8 of U.S. Pat. No. 3,028,751. These continuously oscillating systems, however, are characterized by relatively slow maximum rate of longitudinal movement and a serious lack of reliability due to the increased wear on the components of the transducer head resulting from the continuous motion.